Apparatus for locating hydrocarbon deposits in the earth



April 5, 1938. G. HOV-VELL 2,112,845

APPARATUS FOR LOCATING HYDROCARBON DEPOSITS IN THE EARTH Filed Dec. 2'7,1934.

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/36/// 5 I W 'L 7 1: n illEQz myamu Patented Apr. 5, 1938 PATENT OFFICEAPPARATUS FOR LOCATING HYDROCAR- BON DEPOSITS IN THE EARTH Lynn G.Howell, Houston, Tex., assig'nor to Standard Oil Development Company, acorporation of Delaware Application December 2'7, 1934, Serial No.759,373

1 Claim.

This invention-relates to the location of deposits of hydrocarbonmaterial such as petroleum oil, natural gas or the like beneath thesurface of the ground. Deposits of petroleum oil and/or natural gasusually occur in underground strata under considerable pressure. Theoverlying formations of the ground are permeable to the diffusion of thehydrocarbons from the stratum containing the deposit with a result thatthe soil gases contain measurable amounts of ethane and sometimes butaneand propane. It has been customary in prospecting for oil by suchgeophysical methods as the seismic, gravitational, magnetic andelectrical methods to have for an objective the finding of undergroundstructures favorable to the accumulation of 011.

It is an object of the present invention to locate oil or natural gasdirectly.

Other objects will be apparent from the specification and from theaccompanying drawing in which latter- Fig. 1 is a vertical sectionalview through the ground showing the apparatus in sectional view;

Fig. 2 is a transverse sectional view taken along the line II]I of Fig.1; and

Fig. 3 is a vertical sectional view through a modified form of theapparatus in operative position with respect to the ground.

Referring particularly to the drawing, reference numerals I, I designatethe surface of the ground containing a bore hole 2 The hole 2 ispreferably drilled to a depth of approximately ll feet beneath thesurface of the ground in the territory to be investigated. A tubularmember 5 is disposed in the hole 2 with its bottom wall 6 disposed inspaced relation to the bottom of the hole 2 to form a reservoir .1, thewalls of which constitute the earth stratum 9 in which the hole 2 isdisposed. The wall 6 of the tubular member 5 is provided with an openingi I. A conduit l2 extends into the tubular member 5 on the surface ofthe earth and forms a fluid tight joint with the opening II. An annularcollar I5 is secured in fluid tight relation to the upper end of thetubular member 5 and is provided with downwardly extending annularflange l6 which protrudes into the surface of the ground I, I when thetubular member 5 is in position in the hole 2 to form a seal around thetubular member 5 to prevent air from being drawn into the hole 2 fromthe atmosphere. An additional seal is provided around the hole by meansof plaster of Paris or the like, which is poured around the flangedcollar l5 to form a seal I8 for the hole.

Soil gases are sucked out of, the ground in the vicinity of thereservoir .1 through the following arrangement of parts: A suction pump23 is provided with an inlet pipe 24 which opens into the upper portionof a container 26 through a suitable sealing means 21. Ethyl alcohol orother suitable absorbent. for hydrocarbons well known in the art isdisposed in the container 26 to a level 29 below the inlet of the pipe24. Glass beads 30 or other similar solid particles are disposedin thebody of liquid in the container 26. The conduit l2 opens into thecontainer 25 below the normal level of liquid in the container. Suctionapplied by the pump 23 draws the soil gases from the reservoir 1 throughthe pipe i2 into the body of ethyl alcohol or the like in the container25. The soil gases bubble through the ethyl alcohol whereby thehydrocarbons become dissolved in the solvent and are retained inthecontainer 26 while hydrocarbon free soil gases are, dischargedthrough the pipe 24. The glass beads reduce the size of the bubblespassing through the solvent thereby giving the hydrocarbons a betteropportunity to dissolve in the solvent. If desired, a syphon arrangementor any other means for withdrawing soil gases from the reservoir 1 canbesubstltuted for the pump 23 and some of the advantages of theinvention will be retained.

In carrying out the pumping operation according to the preferredprocedure, a large amount of soil gases is withdrawn from the groundsurrounding the reservoir 1- and is passed through the hydrocarbonsolvent; for example, approximately 400 gallons of soil gases areextracted from the ground during a period which may constitute four daysand four nights of continuous pumping. A partial vacuum is formed in thehole I which prevents faster pumping.

The solvent containing the absorbed hydrocarbons is subjected toanalysis for the primary purpose of identifying and determining thepercentage of ethane in the soil gases. Soil gases adjacent a stratumcontaining petroleum oil and/or natural gas contain measurable amountsof methane, ethane and sometimes butane and propane. Ethane is presentin the soil gases above oil and/ or natural gas deposits in aconcentration of one part in several million parts of soil gas. Also,traces only of ethane or no ethane at all have been found in areas wheretube wells have been drilled to salt water and where therefore it isreasonable to conclude there are no oil or natural gas deposits. The endproduct 01' or: ganic decay is methane. Consequently, methane is foundeverywhere in varying amounts. It is seentherefore that the positiveidentification of ethane in a gas sample obtained from the soil is anindication of the presence of a deposit of oil or natural gas below thepoint at which the gas sample was obtained.

The hydrocarbons absorbed in the solvent are therefore analyzed forhydrocarbons heavier than methane, more particularly ethane and possiblybutane and propane. In one method of analyzing the hydrocarbons theethyl alcohol is subjected to elevated temperatures until the gasesdissolved in the alcohol have been evaporated. These gases are thencooled to about -40 C. whereby some of 'the gases are liquefied and thisliquid is drained off. The liquid is mostly alcohol but some of theheavier hydrocarbons if present will also liquefy at this temperature.The remaining gases are then cooled of! below the boiling point ofethane (whichis -90 C.). The liquid ethane is then drained oil andmeasured.

In making a survey, the bore holes 2 may be disposed approximately 500to 1500 feet apart,

although greater and smaller separations may be employed in differentareas. Reconnaissance surveys using the greater separation of bore holeshave been found advisable. Those areas which are found to have soils ofhigh hydrocarbon and especially ethane content are then worked ingreater detail with the bore holes closer together.

. Referring to Fig. 3, a modified form of the invention is shown inwhich I, l designate the surface of the ground. A tubular member 35 isprovided with an open end adapted to be forced into the ground for asufllcient distance to form good contact all around the end of thetubular member 35 with the ground. The upper end of the tubular member35 is closed as indicated at 36 forming a reservoir 31 which opens uponthe ground. As shown in its preferred embodiment, the tubular member 35has the form of a bell jar. Preferably it has a diameter of from threeto five feet. A convenient method of sealing it with respect to theground is to rotate the tubular member until it makes good contact withthe ground. Plaster of Paris or other suitable sealv ing meansdesignated 39 is then poured around means illustrated in Fig. 1 and likereference numerals are applied to like parts. The means comprises a pump23 having an inlet pipe 24 which opens into the upper portion of acontainer 26, partially filled with suitable solvent or hydrocarbonssuch as ethyl alcohol. Glass beads 30 or the like are disposed in thesolvent. A pipe l2 protrudes into the reservoir 31 at one end and at itsother end opens into the container 25 below the level of the solventtherein.

' It will beunderstood that other methods of analyzing gas samples canbe used and some of the advantages of the invention will be retained.For example, the gas samples can be subjected to:

1. Fractional distillation by means of liquid air.

Combustion. Positive, or canal, ray analysis. Spectral analysis. Highfrequency analysis. Magneto-optic method. Allison. The first two methodsmentioned above are well QUIDWN known in chemical laboratories. Theysufler from the serious disadvantages that rather large samples arerequired and the sensitivity is low. It is impossible by these methodsto work with an accuracy much greater than 0.1 of 1%. Thus ethane mustbe present to the extent of one part in about 1,000 parts of gas. Soilgas samples rarely contain such an abundance of ethane.

The third method of analysis by means of canal or positive rays permitsof the definite identification of the different hydrocarbons in thesample and of estimating their relative abundancies. In this method thegas molecules are shot at a photographic plate by means of an electricaccelerating field through crossed electric and magnetic fields. Themolecules suffer a deflection in both fields, the deflection in theelectric field being proportional to and in the magnetic field 2 1 111?where e=elementary charge E=electric field strength m=molecular weightH=magnetic field strength v=velocity of molecule Molecules of the samemolecular weight are focused on the same spot on the photographic plate.The resolution is very high, being about one part in one thousand parts.This means that particles having weights of 100.0 and 100.1,respectively, can be separated. In the present case, the molecularweight of methane is 16.04, of ethane 30.06, of propane 44.08 and ofbutane 58.10. The relative amount of each constituent of the sample isestimated from the intensities of the different spots or lines on thephotographic plate.

The emission or absorption spectral analysis can also be used to detectthe presence of the hydrocarbons in the soil gases.

The fifth method is based on the fact that the dielectric constants ofthese gases are markedly different and that they also have differentmagnetic susceptibilities. Furthermore, the dielectric constantsincrease in the order air, methane, ethane, propane, butane, while themagnetic susceptibilities decrease in the same order. It is seentherefore that if a sample of air were placed between the plates of acondenser and inside the coil of an'electric oscillating system tuned toa certain high frequency, say one or several million cycles, thefrequency of the system would be higher if methane were substituted forthe air, and progressively higher for ethane, propane and butane. Thecircuit comprising this condenser and coil can be caused to beat againstanother crystal controlled circuit. Assuming now that the crystalcontrolled circuit be caused to oscillate at five million cycles andthat the first circuit be tuned to the same frequency when air has beenplaced between the condenser plates and inside of the coil, it is easyto see that the accuracy would be as great as one part in five million,since a beat frequency of one cycle per second could be observed easily.If, therefore, the substitution of the soil gas sample for the air wouldchange the frequency of the circuit by one cycle, the change could beobserved. It is known also that the ratio of methane to ethane innatural gas is about eight to one. The apparatus can therefore becalibrated with samples known to contain certain amounts of methane andethane.

Another highly desirable method is the magnet0optic due to F. Allison.It is possible to detect one part in one hundred billion by means ofthis arrangement. The method which is described in the literature, forinstance in Physical Review, volume 30, page 66, 1927, volume 31, page313, 1928, and volume 35 page 124, 1930, and elsewhere, is based on thetime lag differences of the Faraday efiect behind the magnetic field inliquids as a function of the chemical compounds dissolved in the liquid.The soil gases are passed through alcohol. '.'I'he hydrocarbons aresoluble in the alcohol while oxygen and nitrogen are insoluble. Thealcohol solution containing the dissolved hydrocarbons is then analyzed.Each chemical compound produces a characteristic minimum of lightintensity at a certain length of light path. These minima disappear whenthe concentration is less than one part in one hundred billion parts.Since ethane is present in the soil gases over deposits of oil and/ornatural gas in greater concentrations, it is seen that the magneto-opticmethod is amply sensitive for its positive identification.

Various-changes may be made within the scope of the appended claims inwhich it is desired to claim all novelty inherent in the invention asbroadly as the prior art permits.

I claim:

In gas extraction apparatus, a tubular mem ber filling the bore of ahole in the surface soil of the earth and having a wall extending acrossits lower end, a tubular casing surrounding the member having adownwardly extending open end embedded in the earth and a closed endcooperating with the tubular member for sealing the member in the bore,and a conduit opening through the wall and adapted to be connected to asource of suction whereby soil gases can be drawn into the conduit.

LYNN G. HOWELL.

